var filechooser = document.getElementById("choose");
    //    用于压缩图片的canvas
    var canvas = document.createElement("canvas");
    var ctx = canvas.getContext('2d');
    //    瓦片canvas
    var tCanvas = document.createElement("canvas");
    var tctx = tCanvas.getContext("2d");
    var maxsize = 2000 * 1024;
    $("#upload").on("click", function () {
        filechooser.click();
    })
    .on("touchstart", function () {
        $(this).addClass("touch")
    })
    .on("touchend", function () {
        $(this).removeClass("touch")
    });
    filechooser.onchange = function () {
        if (!this.files.length) return;
        var files = Array.prototype.slice.call(this.files);
        if (files.length > 9) {
            alert("最多同时只可上传9张图片");
            return;
        }
        files.forEach(function (file, i) {
            if (!/\/(?:jpeg|png|gif)/i.test(file.type)) return;
            var reader = new FileReader();
            var li = document.createElement("li");
//          获取图片大小
            var size = file.size/1024 > 1024 ? (~~(10*file.size/1024/1024))/10 + "MB" :  ~~(file.size/1024) + "KB";
            li.innerHTML = '<div class="progress"><span></span></div><div class="size">'+size+'</div>';
            $(".img-list").html($(li));
            reader.onload = function () {
                var result = this.result;
                var img = new Image();
                img.src = result;
                $(li).css("background-image", "url(" + result + ")");
                //如果图片大小小于100kb，则直接上传
                if (result.length <= maxsize) {
                    img = null;
                    upload(result, file.type, $(li));
                    return;
                }else{
                    //alert('上传图片不能大于500KB');
/*					$('#img_url').val('1');
                    return false;*/
                }
//                图片加载完毕之后进行压缩，然后上传
                if (img.complete) {
                    callback();
                } else {
                    img.onload = callback;
                }
                function callback() {
                    var data = compress(img);
                    upload(data, file.type, $(li));
                    img = null;
                }
            };
            reader.readAsDataURL(file);
        })
    };
    //    使用canvas对大图片进行压缩
    function compress(img) {
        var initSize = img.src.length;
        var width = img.width;
        var height = img.height;
        //如果图片大于四百万像素，计算压缩比并将大小压至400万以下
        var ratio;
        if ((ratio = width * height / 4000000)>1) {
            ratio = Math.sqrt(ratio);
            width /= ratio;
            height /= ratio;
        }else {
            ratio = 1;
        }
        canvas.width = width;
        canvas.height = height;
//        铺底色
        ctx.fillStyle = "#fff";
        ctx.fillRect(0, 0, canvas.width, canvas.height);
        //如果图片像素大于100万则使用瓦片绘制
        var count;
        if ((count = width * height / 1000000) > 1) {
            count = ~~(Math.sqrt(count)+1); //计算要分成多少块瓦片
//            计算每块瓦片的宽和高
            var nw = ~~(width / count);
            var nh = ~~(height / count);
            tCanvas.width = nw;
            tCanvas.height = nh;
            for (var i = 0; i < count; i++) {
                for (var j = 0; j < count; j++) {
                    tctx.drawImage(img, i * nw * ratio, j * nh * ratio, nw * ratio, nh * ratio, 0, 0, nw, nh);
                    ctx.drawImage(tCanvas, i * nw, j * nh, nw, nh);
                }
            }
        } else {
            ctx.drawImage(img, 0, 0, width, height);
        }
        //进行最小压缩
        var ndata = canvas.toDataURL('image/jpeg', 0.1);
        console.log('压缩前：' + initSize);
        console.log('压缩后：' + ndata.length);
        console.log('压缩率：' + ~~(100 * (initSize - ndata.length) / initSize) + "%");
        tCanvas.width = tCanvas.height = canvas.width = canvas.height = 0;
        return ndata;
    }
    //    图片上传，将base64的图片转成二进制对象，塞进formdata上传
    function upload(basestr, type, $li) {
        var text = window.atob(basestr.split(",")[1]);
        var buffer = new Uint8Array(text.length);
        var pecent = 0 , loop = null;
        for (var i = 0; i < text.length; i++) {
            buffer[i] = text.charCodeAt(i);
        }
        var blob = getBlob(buffer, type);
        var xhr = new XMLHttpRequest();
        var formdata = new FormData();
        formdata.append('imagefile', blob);
        xhr.open('post', '/cupload');
        xhr.onreadystatechange = function () {
            if (xhr.readyState == 4 && xhr.status == 200) {
                var jsonData = JSON.parse(xhr.responseText);
                console.log('上传成功：' + jsonData[0].path);
                clearInterval(loop);
                //当收到该消息时上传完毕
                $li.find(".progress span").animate({'width': "100%"}, pecent < 95 ? 200 : 0, function () {
                    $(this).html("上传成功");
                });
                $(".pic-list").append('<a href="' + jsonData[0].path + '">' +jsonData[0].path + '（' + jsonData[0].size+'）<img src="' + jsonData[0].path + '" /></a>');
            }
        };
        //数据发送进度，前50%展示该进度
        xhr.upload.addEventListener('progress', function (e) {
            if (loop) return;
            pecent = ~~(100 * e.loaded / e.total) / 2;
            $li.find(".progress span").css('width', pecent + "%");
            if (pecent == 50) {
                mockProgress();
            }
        }, false);
        //数据后50%用模拟进度
        function mockProgress() {
            if (loop) return;
            loop = setInterval(function () {
                pecent++;
                $li.find(".progress span").css('width', pecent + "%");
                if (pecent == 99) {
                    clearInterval(loop);
                }
            }, 100)
        }
        xhr.send(formdata);
    }
    // 获取blob对象的兼容性写法
    function getBlob(buffer, format){
        var Builder = window.WebKitBlobBuilder || window.MozBlobBuilder;
        if(Builder){
            var builder = new Builder;
            builder.append(buffer);
            return builder.getBlob(format);
        } else {
            return new window.Blob([ buffer ], {type: format});
        }
    }